1. Field of the Invention
The present invention relates to the structure of a ball grid array (BGA) semiconductor package and a method of manufacturing the same.
2. Description of the Related Art
Along with the needs of reduction in size and weight and improvement in function of electronic devices, high density mounting of semiconductor parts into the electronic devices is demanded, and in recent years, there have been required smaller and thinner semiconductor packages suitable for high integration.
In the context of such a trend, various types of semiconductor packages are proposed in response to various applications, such as gull-wing, leadless, BGA, and wafer level. Further, under recent economic environment in which reduction in product price is desired, those semiconductor packages should be provided at a cheaper price together with features in small size and high integration.
In a semiconductor package belonging to a BGA type to which the present invention relates, as illustrated in FIG. 8, the following configuration is provided. That is, the semiconductor package includes: a semiconductor device 1; an adhesive for mounting the semiconductor device 1 to a die pad 23 which is disposed on the substrate 2; bonding wires 6 for connecting the semiconductor device 1 and a plurality of metal lines 20 provided on the substrate 2 to each other; and an encapsulation resin 11 for encapsulating the semiconductor device 1, the adhesive, the bonding wires 6, and the plurality of metal lines 20. On the other surface of the substrate 2, solder balls 22 are formed as external terminals on each of an external connection portion 21. For the substrate 2, a heat-resistant substrate typified by a bismaleimide resin (BT resin) is used. The die pad 23 mounting the semiconductor device 1 and the plurality of metal lines 20 are formed on one surface of the substrate, and the external connection portion 21 is formed on the other surface of the substrate. Via through-holes 4 provided in the substrate 2, each of which is coated with a conduction layer, the respective surfaces are connected to each other. The solder balls 22, which electrically and physically connect the semiconductor encapsulation member and a mounting substrate to each other, are mounted on the external connection portion 21 in a lattice or zigzag arrangement. For example, Japanese Published Patent Application No. 07-193162 and U.S. Pat. No. 5,241,133 disclose such structure.
As described above, in a conventional BGA semiconductor package, unlike a semiconductor package using a metal lead frame, there is used a double-sided substrate or a multilayer wiring substrate, which uses a heat-resistant resin as a base, and hence steps of forming the substrate become complicated. For example, when the substrate is manufactured, it is necessary to manufacture a mask for circuit formation, for forming the wiring on the mounting surface side on which the semiconductor device is mounted, and for forming the external connection terminal on the other side. In addition, during the formation of the substrate, it is necessary to carry out resist coating, exposure and development, resist patterning, forming of the through-hole and plating for electrically connecting the metal lines and the external connection terminals to each other, resist removal processing, and adhesion of the substrates. Accordingly, there has been a problem that the unit price per one substrate becomes more expensive than that in a case where the metal lead frame is used, and the total package cost becomes high.
Further, in the conventional BGA semiconductor package, as the external connection terminal for connection to the mounting substrate, the solder ball is formed and mounted on the substrate. As a formation method therefor, a method is employed in which a minute amount of solder paste or flux is applied to an external connection region of the substrate, and the solder ball is adhered to be connected. In the above-mentioned method, when fluctuations are generated in the application amount of the solder paste or flux, fluctuations in contact area between the solder ball and the external connection region are generated. In a case where the contact area decreases, there has been a problem that the connection strength of the solder ball reduces, which causes defects of the solder ball such as misalignment, formation failure, and drop off, by external vibration or impact.
Further, as described above, in the conventional BGA semiconductor package, the solder ball is formed and mounted on the external connection terminal, and hence the entire thickness of the semiconductor package is increased by the height of the solder ball, and hence there has been a disadvantage that the thinning of the semiconductor package is disturbed.